L. Moro

Harvested power and sensitivity analysis of vibrating shoe-mounted piezoelectric cantilevers

This paper presents a preliminary investigation on energy harvesting from human walking via piezoelectric vibrating cantilevers. Heel accelerations during human gait are established by correlating data gathered from the literature with direct experimental measurements. All the observed relevant features are synthesized in a typical (standard) acceleration signal, used in subsequent numerical simulations. The transient electromechanical response and the harvested power of a shoe-mounted bimorph cantilever excited by the standard acceleration signal is computed by numerical simulations and compared with measurements on a real prototype. A sensitivity analysis is finally developed to estimate the mean harvested power for a wide range of scavenger configurations. Acceptability criteria based on imposed geometrical constraints and resistance strength limits (e.g. fatigue limit) are also established. This analysis allows a quick preliminary screening of harvesting performance of different scavenger configurations.

Simplified numerical approach for the thermo-mechanical analysis of steelmaking components under cyclic loading: an anode for electric arc furnace

ABSTRACT The need of a strong improvement of productivity and reliability led the adoption of advanced modeling techniques in the design of steelmaking plants components. In this work a procedure based on a finite element simulation is proposed in order to perform a durability analysis of an anode for electric arc furnace. This component undergoes cyclic thermal loads, which also produce a partial melting of one part, meanwhile the other is maintained at almost constant temperature by a cooling system. A simplified, but effective, procedure is developed to take into account steel melting during the heating phase. Considering the cyclic loading conditions, several material cyclic plasticity models, and their effect on the thermal fatigue behavior, are also systematically investigated. The proposed approach permits the component fatigue life to be assessed by a simple and fast uncoupled thermo-mechanical simulation in steady-state conditions.

Analytical characterization and experimental validation of performances of piezoelectric vibration energy scavengers

One of the main requirements in wireless sensor operation is the availability of autonomous power sources sufficiently compact to be embedded in the same housing and, when the application involves living people, wearable. A possible technological solution satisfying these needs is energy harvesting from the environment. Vibration energy scavenging is one of the most studied approaches in this frame. In this work the conversion of kinetic into electric energy via piezoelectric coupling in resonant beams is studied. Various design approaches are analyzed and relevant parameters are identified. Numerical methods are applied to stress and strain analyses as well as to evaluate the voltage and charge generated by electromechanical coupling. The aim of the work is increasing the specific power generated per unit of scavenger volume by optimizing its shape. Besides the conventional rectangular geometry proposed in literature, two trapezoidal shapes, namely the direct and the reversed trapezoidal configuration, are analyzed. They are modeled to predict their dynamic behavior and energy conversion performance. Analytical and FEM models are compared and resulting figures of merit are drawn. Results of a preliminary experimental validation are also given. A systematic validation of characteristic specimens via an experimental campaign is ongoing.

Thermo-mechanical analysis of a fire door for naval applications

In this work, the thermo-mechanical response of fire doors for naval application is considered. In order to evaluate their behaviour, fire doors must undergo a standardized fire test. A realistic simulation of the heating process can be useful during the design phase in order to reduce the number of prototypes to be constructed and tested. In this work, a finite element model is developed with the aim of capturing the qualitative behaviour of the fire door and its supporting frame. Two different types of thermal analysis are considered: (1) transient analysis and (2) steady-state analysis. A non-linear mechanical analysis predicts the displacement field that occurs at the end of the heating phase. The adopted model is validated through a comparison with experimental measurements obtained during standard fire tests, confirming that the proposed approach can be a valid tool for the prediction of the thermo-mechanical performance of a naval fire door.

Energy Harvesting with Vibrating Shoe-Mounted Piezoelectric Cantilevers

This chapter presents a study on energy harvesting from human walking via piezoelectric vibrating bimorphs. Heel accelerations are measured and compared with data from literature. All relevant features are summarized in a typical (standard) acceleration signal, used as a reference input in numerical simulations. The transient electromechanical response (beam deflection, output voltage, and average output power) of a shoe-mounted rectangular scavenger excited by the standard acceleration is calculated by numerical simulations. Step-by-step numerical integration is used, as the input is a non-sinusoidal signal and explicit analytical solution is not available. Results from simulations are also validated with measurements on a real shoe-mounted device. A sensitivity analysis is finally performed to find alternative scavenger configurations that could provide increased power levels. Acceptability criteria based on imposed geometrical constraints and material strength limits are also checked. This analysis allows a rapid screening of harvesting performance among a wide set of different scavenger configurations, which allows finding the one providing the largest output power.

On the optimal bending deflection of piezoelectric scavengers

This study aims at exploring the possibility to optimize the electromechanical efficiency of piezoelectric cantilevers by imposing an optimal deflection to classical rectangular devices, rather than designing non-conventional geometries. Focusing on non-vibrating loading conditions, the proposed approach is to apply a constant bending moment to the beam in order to reach the maximum allowable stress on the whole outermost surface. This is realized in practice by pressing the cantilever over a cylindrical-shaped support. Theoretical and numerical models with electromechanical coupling are developed to evaluate the performance improvement compared to the deflection of a classical tip-load configuration. Finally, experimental tests have been performed to further verify the electrical power enhancement given by the proposed optimized layout.

Copper Mold for Continuous Casting of Steel: Modelling Strategies to Assess Thermal Distortion and Durability

In this work the durability assessment and the permanent deformation of a copper mold for continuous casting of steel have been investigated using mathematical models based on the Finite Element method. The cyclic plasticity behavior of the material is represented by a combined kinematic-isotropic model experimentally validated. Results from thermo-mechanical analysis are in good agreement with measurements. In particular, creep effects included into the model permit the evolution of bulging near the meniscus area to be correctly predicted. A life estimation is performed considering strain-life and stress-rupture time curves according to a cumulative damage law.

Thermal distortion in copper moulds for continuous casting of steel: numerical study on creep and plasticity effect

ABSTRACT In this work, the thermal distortion of a copper mould for continuous casting of steel is investigated through numerical models based on the finite element method. Special attention is devoted to the accuracy of the adopted material properties: several elasto-plastic models, with or without creep effects, are considered and compared into the analysis. The early formation of a bulge close to the meniscus is correctly simulated and results are in good agreement with experimental data from the literature.

How Material Properties Affect the Thermal Distortion of a Mold for Continuous Casting of Steel

Copper molds are adopted in continuous casting to provide an initial solidification of steel. The presence of molten steel induces relevant temperature gradients across mold walls. This, in turn, generates high stress levels, exceeding the yielding limit of the material. Recent works confirm that thermal distortion occurs due to both creep and cyclic plasticity. In this work a numerical investigation is developed, simulating the mold behavior under repeated heating and cooling sequences. The aim of this work is to compare the performances in terms of permanent distortion of different copper alloys usually adopted for such application. It can be observed that both material properties and operating temperature have a significant influence in the permanent distortion evolution.